Photovoltaic device forming a glazing

ABSTRACT

The invention concerns a photovoltaic device ( 1 ) comprising a plurality of p-i-n type photovoltaic cells ( 2 ) arranged on a substrate ( 3 ), wherein said cells ( 2 ) are arranged, in the form of a single layer, parallel to one another and the electrical conductive layer ( 7 ) is arranged between the n layer ( 6 ) and the p layer ( 5 ) of each consecutive cell ( 2 ) so as to electrically connect said cells ( 2 ) in series. The invention also concerns the use of such a device ( 1 ) as glazing, a method for making such a device ( 1 ), a method for controlling a transparent photovoltaic device ( 1 ) as well as an installation for implementing said control method.

This application is a divisional application of Ser. No. 10/525,522,filed Jan. 3, 2006.

The invention concerns a photovoltaic device, the use of said device asglazing, a method for producing said device, an installation forimplementing said method, a method for controlling a transparentphotovoltaic device, as well as an installation for implementing saidcontrol method.

The present invention concerns a photovoltaic device in which severalp-i-n type photovoltaic cells are ranged parallel to one another on asubstrate, said cells being electrically connected in series.

It can normally be applied when the substrate is a tinted glass plate tobe used for the external glazing of architectural buildings.

These tinted glass plates arm widely used in the construction of officebuildings, schools, hospitals and other buildings for attenuating thedazzling light, ensure absorption of one portion of the heat radiated bythe sun and thus reduce the costs of carrying out air-conditioning.

In a large number of cases, polished plates for windows encompass anentire building and, owing to their exposure to solar radiation, couldconstitute a large source of electric energy if they were provided witha photovoltaic device.

Preliminary calculations indicate that, even with relatively lowphotovoltaic efficiencys, it would be possible to sufficiently generatecurrent to satisfy part, if not all, the electric current needs of thebuilding.

The document U.S. Pat. No. 4,271,328 describes a photovoltaic devicehaving a tandem structure in which two, three or more than threephotovoltaic unit cells each comprising a p-i-n semi-conductive joiningpoint are stacked in series along the light propagation direction.

In this type of device, the light leaving the unit photovoltaic cell,without taking part in photovoltaic action, can be absorbed in thefollowing photovoltaic cell so as to improve the overall photovoltaicefficiency of the device.

But the stacking of the photovoltaic cells along the propagationdirection of the light has the drawback that an increase of thephotovoltaic efficiency occurs to the detriment of the transparency ofthe photovoltaic device.

Thus, it is difficult to consider having these devices arranged on aglass substrate for glazing a building in that it needs to possesssufficient transparency for it to be used.

In addition, currently available photovoltaic devices are clearlylimited as regards the tension and output.

In fact, as the incident light is successively absorbed by the variouslayers of the photovoltaic cell the final cell receives less photonsthan the first so that its output is not optimum.

Therefore, the invention seeks to resolve these drawbacks by offering aphotovoltaic device which is sufficiently transparent so as to be usedas a glazing glass.

In addition, the outgoing electric voltage and the photovoltaicefficiency of the device of the invention are improved with respect tothose of the prior art.

To this effect and according to a first characteristic, the inventionconcerns a photovoltaic device including a plurality of p-i-n typephotovoltaic cells arranged on a substrate in which said cells arearranged in the form of a single layer, are parallel to one another andin that an electric conductive layer is placed between the n layer andthe p layer of each consecutive cell so as to electrically connect saidcells in series.

In a variant, the device is transparent to light rays.

According to a second characteristic, the invention concerns the use ofthis device as glazing for architectural buildings in which thesubstrate is formed by the glazing.

In a variant, the photovoltaic cells cover approximately the entiresurface of the glazing so as to increase the amount of current generatedper square metre of glazing.

According to a third characteristic, the invention concerns a method forproducing a device as described above in which the various layers arelaid using the chemical vapour phase deposit method.

According to one embodiment of the method, after preparing thesubstrate, the various layers are laid by using:

-   -   a first mask whose openings correspond to the electric        conductive layers;    -   a second mask whose openings correspond to the n type layers;    -   a third mask whose openings correspond to the p type layers;    -   a fourth mask whose openings correspond to the i type layers,        said masks being arranged on the glass plate so as to allow        depositing of the respective layers.

In one variant, the first, second, third and fourth masks are usedsuccessively.

According to a fourth characteristic, the invention concerns aninstallation for implementing the method described above, saidinstallation including a working space in which the substrate is placed,a chamber surrounding the working space, heating means, a separation ofthe working space and a cooling chamber.

According to a fifth characteristic, the invention concerns a method foroptically controlling a transparent device such as the one describedabove in which the image of the device is observed on successive narrowstrips along one or several segments of a specific line covering thedesired width for examination, said image of the device being projectedto via transparency onto a nearby screen which retransmit it by onlyilluminating the device on one zone, also narrow, covering said segmentsof the read line.

According to a sixth characteristic, the invention concerns aninstallation for implementing said control method, said installationfurther including presentation elements of the device:

-   -   a translucent diffusing screen placed opposite the position of        the device as near as reasonably possible so as to have it avoid        the trajectory of the latter concerning its movement of being        placed on the installation and then removed;    -   a linear camera receiver targeting the screen via its rear face;    -   a fixed light transmitter placed beyond the location of the        device so as to sufficiently homogeneously illuminate on the        screen a narrow zone covering the selected segment(s) for        examination and preferably by forming a spread-out thin beam        operating via transparency.

Other objects and advantages of the invention shall appear on a readingof the following description with reference to the accompanyingdrawings.

FIG. 1 is a rear perspective diagrammatic view partially showing aphotovoltaic device including several unit photovoltaic cells arrangedparallel to one another on a glass substrate.

FIG. 2 is a partially cutaway diagrammatic view showing the photovoltaicdevice of FIG. 1.

With reference to the figures, a photovoltaic device 1 is describedincluding several unit photovoltaic cells 2 arranged parallel to oneanother on a substrate 3 formed of a first glass plate.

Each photovoltaic cell 2 includes a p-i-n type semi-conductive joiningpoint in which an i 4 type optically active layer is surrounded byrespectively a p 5 type semi-conductive layer and an n 6 typesemi-conductive layer.

To improve understanding of the invention, the layer i is representedenlarged and exploded on the figures, but needs to be viewed as beingplaced between the layers n and p 6, 5.

When this device 1 is subjected to an incident solar radiation, electronphoto-carriers and holes are created in the i 4 type optically activelayer.

Under the action of the electric field existing between the p 5 typelayer and the n 6 type layer, the electrons move towards the n 6 typelayer, whereas the holes move towards the p 5 type layer.

In this photovoltaic cell 2, it is therefore necessary to have, not onlyone optically active i 4 type layer actually taking part in the creationof electric energy in which no doping impurity is approximately present,but also layers doped by n 6 and p 5 type impurities so as to create anelectric joining field.

When the circuit is closed by means of electric conductors 7 placed incontact with respectively the n 6 type layer and the p 5 type layer,there is then circulation of current in an external circuit (not shown).

The photovoltaic device 1 is thus able to convert the light energyemitted by the sun into electricity and the output of this conversioncorresponds to the quantity of current obtained for a given light flow.

The layers p, i and n 5, 4, 6 of a photovoltaic cell 2 are arrangedparallel to one another on the substrate 3 in the form of a single layerso that the photovoltaic action of each of the cells 2 is generated bythe incident light.

This arrangement makes it possible to increase the photovoltaicefficiency since the optically active layer 4 of each photovoltaic cell2 is subjected to the incident solar radiation without a portion of thelatter having been absorbed by another layer of the cell 2 or by anothercell 2 of the device 1.

Thus, the number of photo-carriers generated by the i 4 type layer ofeach photovoltaic cell 2 of the device 1 is optimum and thus the totalphotovoltaic efficiency of the device 1 increases.

Moreover, by adjusting the width of the prohibited optical strip of theoptically active layer 4, it is possible to shift the peak wavelengthfrom its photosensitivity so as to be able to be further increase thephotovoltaic efficiency.

In addition, this embodiment is able to obtain a photovoltaic device 1which is sufficiently transparent so as to be used as glazing forarchitectural buildings.

To this effect and after a large number of tests, the applicant hasdiscovered that a photovoltaic cell 2 including gallium as an i 4 typelayer and a p-n 5, 6 homojoining point formed of gallium arsenide givinggood results in terns of total photovoltaic efficiency and electricoutput voltage.

For example, the p doping of gallium arsenide can be embodied byincorporating in it about 10% atomic weight of carbon and the n dopingby incorporating with it about 10% atomic weight of nitrogen.

As these various types of doping are already known, no further detailsshall be given concerning this description.

In addition to their excellent electronic characteristics, the materialsused, when they are laid in thin layers, exhibit sufficient transparencyso as to be able to be used as glazing.

To this effect, the thickness of the layers p, i and n 5, 4, 6 can beabout 25 Angstroms.

In addition and contrary in particular to photovoltaic devices usingamorphous silicon, the photovoltaic efficiency of the device 1 does notlower significantly when it is subjected to an intense light radiationfor a long period. This characteristic is obtained by virtue of theslight ageing of the gallium under the effect of the photons.

In the embodiment shown on the figures, the photovoltaic cells 2 areelectrically connected in series by conductors 7 placed between each ofthem in thin layers on the substrate 3.

In one embodiment, the electric conductors 7 are formed of a layer ofcopper having approximately the same thickness as the layers p, i and n,said layer being respectively in contact with the layer p 5 and thelayer n 6 of two consecutive cells 2.

In addition, the photovoltaic device 1 includes connection means 8 withan external circuit so as to collect the generated current. Theconnection means 8 are placed on the substrate 3, by example by etching,and in contact with the electric conductors 7 of the extremephotovoltaic cells 2 of the device 1.

In the embodiment shown exploded on the figures, a second glass plate 9identical to the first is placed on the device 1 and in contact with thephotovoltaic cells 2 so as to protect them.

During functioning of the device 1, the incident light (see the arrow onFIG. 2) is transmitted via the second glass plate 9 to all the type i 4layers of the various unit cells 2 so as to create photocarriers which,under the action of the electric joining field, generate current in theset of cells 2 connected in series, the current then being recovered inthe external circuit by means of connection means 8, the light thenbeing transmitted through the device 1 (see the arrow on FIG. 2), thatis towards the inside of the building via the substrate 3 and to be usedas glazing.

As part of its use as glazing, another advantage of the device 1 isthat, apart from the electric energy production, it is able to absorbthe calorific energy via the Peltier effect and accordingly furtherreduce exploitation of the air-conditioning costs of buildings in whichit is installed.

There follows below a description of the method for obtaining aphotovoltaic device 1 according to the invention.

According to this method, the cells 2 can be embodied simultaneouslywith their electric circuit 7 so that the completed device 1 is ready tobe installed.

The photovoltaic cells 2 and the electric conductors 7 are embodied inthe form of thin coatings which are applied by means of vapour phasechemical depositing (CVD) directly on the first glass plate 3.

Owing to its excellent surface condition and its other properties, theglass constitutes the best support for applying thin coatings. It is anonconductor, resists corrosion and bad weather conditions and its lowcoefficient of expansion reduces the risk of fracturing of the coatingsbound on its surface and when it is heated, the melting point of theglass corresponds to the melting points of the other active materialsconstituting the photovoltaic cells 2.

However and with the aim of preventing the migration of the sodium ionsof the glass towards the photovoltaic cells 2 they could contaminate, itis desirable to render passive the surface of the glass, for examplewith an aluminium oxide prior to depositing of the various layersforming the cells 2.

Although the invention is applicable in particular to the field ofglazing, the cells 2 can be deposited on a substrate 3 other than glass,for example a polished metal or formed of glass fibres, as a specificsubstrate able to be used for other applications.

In particular, satisfactory results have been obtained by depositing thephotovoltaic cells 2 on polished metal.

The gas phase chemical depositing of metal materials or semi-conductorsis already known thus its principle shall not be detailed in thisdescription.

A specific and simple implementation method is a plasma spraying method,for example the high frequency heating of the materials constituting thecells 3 and the conductors 7 in the presence of an atmosphere free fromhydrogen.

During implementing this method, masks are used which are arranged onthe substrate 3 so as to deposit the gaseous compound on the desiredlocation(s) and then separated from it after this depositing.

The masks can be either semi-permanent metal, carbon or plastic or bedisposable after usage when made of impregnated paper or plastic.

The suggestion of using a mask to be disposed of after usage resides inthe fact that, when the layers are deposited, material accumulates alongthe periphery of the openings of the mask so that following repeateduses, the shape of the openings has modified. Thus, the permanent masksneed to be cleaned after each use.

The disposable mask has the advantage of being clean for eachapplication.

Irrespective of the type of mask used, the latter needs to be fixed tothe substrate 3 before each stage of depositing, this fixing being ableto be embodied either automatically or manually.

The semi-permanent masks can be produced in metal or plastic materialsimpregnated with carbon or graphite, provided the materials to bedeposited does not adhere or adhere only slightly above.

The masks to be disposed of after usage can be made of paper, theopenings being cut or pierced in a roll of paper which continuouslyunwinds or in individual sheets cut to the dimensions of the substrate.For example, these masks can be coated with an adherent adhesive viapressure so as to be able to associate them temporarily with thesubstrate 3 for carrying out depositing. In this case, the adhesive canbe laid in the form of points whose number and placing are arranged toallow association without damaging the substrate 3.

In addition, during the association stage and then disassociation of themask from the substrate 3, it is essential to avoid any contamination orscratches of the substrate 3 which would adversely affect theperformances of the photovolaic device 1.

Disposable masks have the advantage of allowing inspection of theproduct between application of the various layers, a different mask thenbeing used for depositing each layer.

However and in the case where the substrate needs to be heated during orafter the depositing of the layers, the choice of the material formingthe mask needs to be made so that it does not deteriorate or warp underthe effect of the temperature.

The first stage of the obtaining method of the photovoltaic device 1 isthe preparation of the glass plate as a substrate 3.

During this stage, the glass plate is cut to the desired dimensions, theedges are trimmed and after cleaning at least the surface for receivingthe cells 2 is rendered passive, for example with an aluminium oxide.

Next, the various layers of the photovoltaic device 1 are deposited byusing:

-   -   a first mask whose openings correspond to the layers of the        electric conductors 7, said mask being placed on the glass        plate, and copper is deposited by vapour phase chemical        depositing, for example with a thickness of about 25 Angstroms;    -   a second mask whose openings correspond to the type n 6 layers,        said mask being arranged on the glass plate and then type n        gallium arsenide is deposited by vapour phase chemical        depositing, for example with a thickness of about 25 Angstroms;    -   a third mask whose openings correspond to the type p 5 layers,        said mask being placed on the glass plate and then type p        gallium arsenide is deposited by vapour phase chemical        depositing, for example with a thickness of about 25 Angstroms;    -   a fourth mask whose openings correspond to the type i 4 layers,        said mask being placed on the glass plate, and then the gallium        is deposited by vapour phase chemical depositing, for example        with a thickness of about 25 Angstroms.

Once the photovoltaic device 1 is embodied, the connection means 8 canbe placed and then also the second glass plate 9 so as to obtain aphotovoltaic device 1 forming the glazing glass which is ready to bemounted in architectural buildings.

There follows below a description of an installation for implementingthe method for obtaining the photovoltaic device 1.

This type of installation typically includes a working space in whichthe substrate 32 is placed, a chamber which surrounds the working space,heating means, insulation of the working space, and a cooling chamber.

The transfer of beat from the working space to the wall of the chamberis basically effected by means of beat conduction, convection andradiation.

During placing under vacuum, the transfer of heat only takes place viaradiation and the heat conduction of solid components and, when thepressure increases, the transfer of heat increases towards the wall ofthe chamber.

Damaging effects, such as an exaggerated temperature of the wall of thechamber having an effect of limiting the lifetime and reliability of theinstallation or an excessive consumption of energy or even an inadequatehomogeneity of the temperature of the working space, appear if thistransfer of heat is not controlled or reduced.

These installations are described in the documents DE-30 14 691 and U.S.Pat. No. 4,398,702. So as to mitigate the drawbacks mentioned above, inaddition to the characteristics described in these documents, theinvention specifies that:

-   -   1) an additional insulation needs to be placed in front of the        wall of the chamber;    -   2) the insulation of the wall of the chamber is embodied with        sheets and/or metal plates;    -   3) the insulation of the working space is constituted either by        hard felt plates with graphite sheet plating impermeable to the        gases, said plates being placed on the lateral walls, the upper        covering wall and the frontal walls, or the upper edges and        joints are covered with graphite corner-shaped sections        reinforced by carbon fibres so as to obtain imperviousness with        respect to the passages of gases, whereas the lower edges are        open so as to allow evacuation of said gases;    -   4) the corner-shaped sections are arranged alternately repeated        between the hard felt plates so as to establish a labyrinth type        imperviousness;    -   5) the frontal edges of the insulation of the working space        and/or the conjugated surfaces are fixed in the reinforced        graphite sections by carbon fibres;    -   6) partitions are placed as anti-convection barriers between the        insulation of the working space and the insulation of the wall        of the chamber;    -   7) the partitions are made of a metallic material in the form of        sheets and/or steel plates;    -   8) an additional cooling by water is placed between the        insulation of the wall of the chamber and the wall of the        chamber    -   9) the additional cooling by water is placed in the upper half        of the chamber close to the flange and the cover.

The first and second characteristics have the effect of creating a sharpfall of temperature at the level of the internal wall of the chamber soas to be able to maintain a low temperature at this location.

With the characteristics 3) and 4), insulation is improved atparticularly critical locations. For example, in the case where theworking space has a polygonal section at the level of the joining pointbetween two walls. In fact, these joining points exhibit residualintervals which, in installations of the prior art, increase over aperiod of time and thus can be the cause of a defective insulation.

This damaging effect can be avoided by covering the intervals, but thencertain difficulties appear. In fact, from the point of view of shaping,metal sheets would be suitable for covering the angles and edges, but asthe insulation of the working space is constituted by graphite felt, acovering with narrow contact would lead to chemical reactions and,during heat expansion, to mechanical stresses which adversely affect theefficiency of the installation.

These difficulties ran be overcome if, for covering, the same materialis used as the one constituting insulation of the working space, namelygraphite. However, conventional graphite materials are excluded as theyare unsuitable to embody sealed joints in the corners and on the edgeson account of their excessive fragility.

Graphite materials reinforced by carbon fibres and able to be embodiedaccording to any selected section are nevertheless available. The use ofcorner-shaped sections constituted by this material for covering theresidual intervals at the level of the corners and edges constitutes thebest possible solution to the problem mentioned above.

In addition, if these elements are arranged in several copies betweenthe various insulation layers of the working space, a labyrinth typesealing is obtained and accordingly an additional improvement ofinsulation of the working space.

Similar critical locations are found on the frontal edges of theinsulation of the working space where, owing to frequent openings andclosings, the surfaces used for insulation are exposed to excessivewear. The arrangement shown at 5) can resolve this problem and canobtain reliable and effective insulation.

The partitions described at 6) and 7) prevent convection and thus reducethe transfer of heat from insulation of the working space towards thewall of the chamber or towards the insulation of the wall of thechamber.

An additional cooling located on the sides of the cover of the chamberis described at the points 8) and 9). This cooling is necessary as thenormal cooling of the chamber is inadequate owing to the considerablethickness of the wall where the flange and cover are located.

During functioning and in conditions of equilibrium, a constanttemperature exists on the working space owing firstly to the quantity ofheat brought by the heating means, and secondly the amount of heatevacuated outside the installation from the working space towards thewall of the chamber by means of conduction, radiation and/or heatconvection.

By virtue of the characteristics indicated at points 1) and 2), areduction of the convection in front of the wall of the chamber isobtained and as a result the drawing up of a higher temperature gradientso that the temperature in front of the wall of the chamber is reduced.

By means of the characteristics 3) to 5), the quantity of heattransmitted by convection from the working space to the other volumes ofthe chamber is reduced.

By virtue of the characteristics 6) and 7), the component of thequantity of heat transmitted by convection is reduced.

The characteristics 8) and 9), by means of improving heat evacuation,have the effect of reducing the temperatures of the chamber where theflange and cover are situated.

There follows below a description of the method for the optical controlof a transparent photovoltaic device 1.

The term ‘transparent’ relates to a device 1 through which the light isable to pass by allowing the objects located behind to appear withsufficient cleanness.

The oldest technical methods for examining translucent bodies used toconsist of examining them by turning them by hand in front of lightsource, preferably constituted by a strongly lit white background so asto observe them as they pass.

The modern control methods electronically analyse stage by stage thefluctuations of a signal retransmitted by the body from a suitable lightsource. They are especially used for controlling articles having atleast a partially axial system, in particular articles made of glass,such as bottles, drinking glasses, or even made of plastic.

As regards reading a relatively wide zone of the surface, this iscarried out column by column by strictly analysing the successive stripsof the wall in successive unwinding planes parallel to the axis.

A synthesis is then carried out according to all types of criteria so asvisualise the position, extent and in particular the intensity of eachdefect, but generally speaking, neither the selected methods of analysisnor synthesis directly depend on the mode of observation. In this case,they are outside the objective of the method and shall not be describedbelow.

The most precise methods operate at a fixed station or sometimes withthe aid of tracking devices and, as regards lighting, generally scan theheight of the article with a narrow brush such as a synchronisedquasi-punctual laser brush whilst it rotates by a full revolution.

A simplification consists of illuminating the entire zone to be examinedby placing the device 1 in front of permanent light source possiblymodulated, regardless of whether it is a concentrated source or one witha light background. It is still possible to operate by rotation on onerevolution or only on moving past but under several additional angles,and if essential under a single one. A more concise analysis is thusobtained but faster and which is sufficient in a large number of cases.

As regards hollow articles, the light only makes one crossing so thatthe image observed then in some way forms the shadow of a line of thewall close to the screen. More frequently however, it makes twocrossings so that the image then also reflects some defects of the mostdistant wall.

The method of the invention is drawn from this method whilst allowing aprecise analysis of the device to be verified. It consists of observingon successive narrow strips along one or several segment(s) of aspecific line covering the desired test width the image of the device 1projected by transparency onto a nearby screen which rediffuses it byonly illuminating the device 1 on a narrow zone covering said segmentsof the reading line.

Generally speaking, it is preferable, especially for rotating devices 1,to carry out rotation along the meridians or successive main generatinglines.

The description mainly refers to this type of control, but in certaincases it could be operated during moving past, transposition beingimmediate.

So as to illuminate the various segments of the inspection zone, it ispreferable to use a directed beam having, at least transversally, asmall opening. Finally, the image formed on the screen shall almostinevitably remain observed via the “rear” face of the latter, namely theone which does not face the device 1, that is through this screen.

Apart from the conventional elements of the device 1 at the controlstation, an installation for implementing the optical control methodshall thus include a fixed station or, if appropriate, on a trackermounting:

-   -   a translucent diffusing screen placed opposite the position of        the device 1 as close as reasonably possible so as to in        particular have it avoid the path of the latter in its placing        movement on the installation and then of evacuation,    -   a linear camera receiver aimed at the screen via its rear face,    -   a fixed light transmitter placed beyond the location of the        device 1 so as to homogeneously illuminate on the screen a        narrow zone covering the selected inspection segment(s)        preferably by forming a spread out thin beam operating by        transparency.

As regards the devices 1 with total or partial axial symmetry, such asmost glazing glass, the presentation and mainly the rotating elementsare usually associated with a reference horizontal plate and all theoptical elements of the device shall be placed along a given plane ofsymmetry of the station perpendicular to the crossing path of the latteraimed at an inspection line principally close enough to a meridian. Asmost current machines use plate or vertical axis barrel conveyors, thisplane shall thus be a vertical plane passing through the axis of themachine. However, it is possible to operate obliquely, and in separateplanes close to the latter, possibly slanted on the axis if necessarythrough at least one wall.

In practice, a receiver comprising a camera combing a conventional lensand a photosensitive element constituted by a single diode rectilinearbar is suitable for observing with the desired precision the imagesupplied by all the zones to be examined.

Advantageously, it shall be provided with a return mirror to enable itto be orientated so as to be able to place it at the desired distance soas to cover the entire height to be controlled without creatingexcessive lateral congestion. It is also possible to use a optical fibrelight guide.

The screen could be constituted only of a narrow translucent flat smallplate formed of an opal or glass sheet on its front face, but ifnecessary, it could also include a juxtaposition of the faces orientedaccording to a basically prismatic position along the profile of thepath in question. As a variant, it can have a curved surface, namelythat of a cross section or at least not very oblique of a cylinder withan axis perpendicular to the plane of symmetry. Thus, it shall followthe shape of the device 1 at a distance of for example between 1 and 3centimetres. This distance shall remain constant without however therebeing any, excessive winding creating any difficulties, either asregards the construction or even observing the device as regards thelighting or focussing angles or otherwise the field depth.

The thinner the screen is, the better shall be the precision andsensitivity of analysis.

As regards the transmitter, a single concentrated light source sufficeswhich is diaphragmed by a window which creates a thin beam.

However, it is also possible to use a projector using an optical systemwith linear or punctual source emitting a narrow beam basicallydiaphragmed by a flat beam so as to illuminate the selected inspectionsegments by passing through the axis of symmetry of the device 1 or atleast close to it. So as to enable the screen to retransmit a uniformlight flow towards the receiver a sufficiently uniform luminous flux, asa variant, several of these projectors can be associated, eachilluminating its own section under an adjustable intensity with apossible covering of successive radiant fields so as to generate auniform radiant field or even correct the influence of angular gaps.This transmitter could also be equipped with a return optical system.

As already specified above, for reasons of gaining advantages, such asobtaining more space, the positions of the elements could be spaced fromthe said symmetry with respect to a main section, the receiver and thetransmitter being adjustable and focussed on the screen according tonearby but different average illumination and observation planes, bothbeing basically parallel to the axis of the device 1 in the controlposition or slightly slanted on it.

There now follows a description of first and second embodiments of theinstallation for implementing the method for optically controlling atransparent device 1.

The device 1 is mounted on a conventional machine, the device 1 restingon a horizontal plate so the its axis is vertical. It is driven by astar wheel carrying rollers which enable an external counter-roller tomake it rotate at the control station. This concerns an arrangementselected for convenience and thus is not described in detail.

In the first embodiment, the screen is formed of a narrow cylindricallycurved translucent thin plate made of opal plastic placed transversallyto the plane of symmetry along the main generating line or externalmedian of the device 1 in a control position without moreover exactlyfollowing its curve.

The receiver comprises a camera whose lens is placed in front ofphotosensitive diode rectilinear bar connected to a preamplifier. Thisunit is situated inside a box bearing a return mirror which, when facingthe rear face of the screen, makes it possible to vertically orientatethe lens so as to reduce the horizontal spatial requirement and to focusit on the screen.

The transmitter is formed of a simple lamp fitted with a reflector andplaced towards the inside of the machine under the reference plate wherea rectilinear window diaphragms its light into a thin beam forming onthe screen astride the median plane a light zone which covers thesegment to be examined.

In the presence of a device 1, a single wall is crossed so that anypossible defects of the device shall be expressed by local variations ofillumination. The latter detected by the device shall indicate thesedefects and, if appropriate, a suitably time delay device shall thenmake it possible to move away the device 1.

In the second embodiment, the translucent screen is formed of a flatglass plate unpolished on its front face orientated towards the device 1and passing close enough to the corresponding main generating line.

The receiver and transmitter are thus placed side by side above the pathof the device 1.

The receiver, similar to that of the first embodiment, has its cameradirected from top to bottom towards a reflecting mirror slanted at about40° from vertical in an extremely slight oblique transversalarrangement, which makes it possible to focus it on the screen along theclosest generating line by appropriately orientating the diode bar. Thetransmitter includes a projector directed from top to bottom towards areflecting mirror, also slightly moved out of centre and slanted atabout 40° from vertical so as to fold up the beam illuminating thescreen in a slightly descending direction.

As for the receiver, said arrangement makes it possible to move theprojector to a sufficient distance without taking up any excessivespace.

A slot is made in the plate so as to enable the light rays to passthrough.

The projector with a conventional structure has a lamp and a capacitorformed of two lens currently associated with a concave mirror so as toform at a short distance the image of its filament, the light beingpicked up by a lens.

As the source is not punctual, the mirror, despite its shape, would onlydiaphragm imperfectly into a flat beam the beam emitted by theprojector. This is why it is necessary to adjust the lens on a fielddiaphragm bearing a slot, for example measuring 0.7 mm on 15 mm, placedclose to the image but slightly put out-of-focus so that in the regionof the screen in the absence of the device 1 to be controlled, a narrowrectangular image is formed fifteen to twenty times greater orpractically with virtually homogeneous luminosity.

1. Installation for thin-film-deposition using a chemical vapourdeposition technique, which type of installation includes a processspace in which the substrate is placed on which the thin films are to bedeposited, a chamber which surrounds the process space, heating means,insulation of the process space, and a cooling chamber, wherein anadditional insulation is placed in front of the wall of the chamber, theinsulation of the wall of the chamber is embodied with sheets of metaland/or steel plates, and the insulation of the process space isconstituted by hard felt plates with graphite sheet plating impermeableto the gases, said plates being placed on the lateral walls, the uppercovering wall and the frontal walls, whereby the upper edges and jointsare covered with graphite corner-shaped sections reinforced by carbonfibres so as to obtain imperviousness with respect to the passage ofgases, whereas the lower edges are open so as to allow evacuation ofsaid gases.
 2. Installation according to claim 1, wherein thecorner-shaped sections are fitted alternately repeated between the hardfelt plates so as to provide a labyrinth type imperviousness. 3.Installation according to claim 1, wherein the front edges of theinsulation of the process space and/or the conjugated surfaces are fixedin the graphite sections reinforced by carbon fibres.
 4. Installationaccording to claim 1, wherein partitions are fitted as anti-convectionbarriers between the insulation of the process space and the insulationof the wall of the chamber.
 5. Installation according to claim 4,wherein the partitions are made of metal in the form of sheets and/orsteel plates,
 6. Installation according to claim 1, wherein anadditional cooling by water is provided between the insulation of thewall of the chamber and the chamber.
 7. Installation according to claim6, wherein the additional water cooling is provided in the upper half ofthe chamber in the area of the flange and the cover.